Air conditioning system

ABSTRACT

An air conditioning system including a variable speed compressor configured to operator at faster and slower speeds. The system includes an evaporator and a thermal expansion valve for regulating the flow of a refrigerant from the compressor to the evaporator. The system includes a flow restricting device in a flow path from the thermal expansion valve to the evaporator thereby increasing the efficiency of the system when the compressor is operating at slower speeds.

BACKGROUND

The present disclosure relates generally to the field of heating andcooling systems. In particular, the disclosure more specifically relatesto a variable capacity evaporator employed in an air conditioningsystem.

Many air conditioning systems include a metering device (e.g., anexpansion valve) which regulates the flow of liquid refrigerant into anevaporator. These devices may include simple capillary tubes,thermostatic expansion valves, constant pressure valves, electronicneedle valves, and other components. The metering devices tend to becarefully matched to the evaporator and other system components soenough refrigerant is fed to fill the evaporator but not so much thatliquid refrigerant is allowed to flow out the exit tube. The amount ofrefrigerant required may depend on the operating temperature and coolingcapacity of the system. Metering in too little refrigerant may reducethe efficiency of the system by failing to take full advantage of theheat exchange surface offered by the evaporator. Conversely, metering intoo much refrigerant may allow liquid to pass through the evaporator andinto the compressor, risking damage

To prevent such problems, conventional systems may employ a meteringdevice and evaporator that work together to ensure about 100%evaporation of the liquid refrigerant within the evaporator. Such adesign typically includes the ability to maintain a stable preset“superheat”—the temperature difference between the refrigerant boilingtemperature and the temperature of the gas as it exits the evaporator.

Standard industry practice, both in the design of the metering devicesand air conditioning system itself, generally increases the energyefficiency of the system by ensuring a sufficiently regulated supply ofrefrigerant into the evaporator to maintain a relatively stablesuperheat of the refrigerant under most conditions.

SUMMARY

According to a disclosed embodiment an air conditioning system isprovided. The system includes an evaporator containing refrigerant and ametering device for regulating the flow of refrigerant into theevaporator. The metering device is configured to regulate the flow theevaporator based at least in part on the pressure sensed in a flow pathto the evaporator. The system also includes a compressor for compressingrefrigerant and providing liquid refrigerant to the metering device. Thesystem is configured so that refrigerant flowing from the meteringdevice into the evaporator passes through a flow regulating devicelocated in the flow path.

According to another disclosed embodiment an air conditioning systemincluding a variable speed compressor configured to operator at fasterand slower speeds is provided. The system also includes an evaporatorand a thermal expansion valve for regulating the flow of a refrigerantfrom the compressor to the evaporator. The thermal expansion valve isconfigured to control the flow of the refrigerant into the evaporatorbased on a temperature sensed at the outlet of the evaporator and apressure sensed at the inlet to the evaporator. The system includes aflow restriction device in a flow path from the thermal expansion valveto the evaporator thereby increasing the efficiency of the system whenthe compressor is operating at slower speeds.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages will become apparentfrom the following description, appended claims, and the accompanyingexemplary embodiments shown in the drawings, which are briefly describedbelow.

FIG. 1 is a schematic diagram of a variable capacity evaporator systemaccording to one exemplary embodiment.

FIG. 2 is a schematic diagram of the variable capacity evaporator systemof FIG. 1 with an increased compressor speed according to one exemplaryembodiment.

FIG. 3 is a schematic diagram of the variable capacity evaporator systemof FIG. 1 with a decreased compressor speed according to one exemplaryembodiment.

DETAILED DESCRIPTION

The energy efficiency of small and mid-size air conditioning systems canbe improved through the use of variable-speed compressors. The use ofvariable speed compressors offers the ability to more closely match thecapacity of the system with the varying load resulting in lower energyconsumption. In such systems, the compressor changes speed so that theevaporator temperature remains stable as the heat load changes. As withnon-variable speed systems, the role of the metering device remains thesame—to maintain a relatively stable superheat setting.

Air conditioning systems employing variable speed compressors areintended to produce a required cooling capacity with a minimum use ofinput power. To accomplish this, as the load changes, the systemcapacity changes as well. In this way, the heat load and system capacityremain in relative balance. This approach to maximizing energyefficiency may be appropriate when unlimited electrical power isavailable and the primary goal of the air conditioning system is toprovide sufficient cooling power to match the heat load. While it may bedesirable to reduce the power needed to provide this cooling, the energyconsumption is generally secondary to the primary goal of providing fullcooling power.

When an air conditioning system is powered by a limited energy source(e.g., a battery-power system), the availability of power may takepriority over the desire to provide full cooling capacity. In such asystem it may be more desirable to provide a modest amount of coolingover a longer period of time than to provide full cooling capacity for ashorter period. The priority may become the rate of energy consumptionwhile the maximization of effective cooling is a secondaryconsideration.

In a variable-speed high efficiency air conditioning system thecompressor speed is varied to match a changing heat load. This typicallyresults in a more stable and optimally determined evaporatortemperature. The speed may vary from slower to faster speeds. The speedmay be continuously variable or variable between certain predeterminedspeeds.

However, in a limited energy capacity system, the compressor speed isvaried according to the availability of electrical power regardless ofthe heat load. The result is that the evaporator temperature may rise toan unacceptably high level. This high evaporator temperature may resultin poor cooling performance due to excessively high discharge airtemperature.

To maintain acceptable cooling performance when the compressor speed isreduced (i.e., minimizing power draw) and while the heat load remainsrelatively high, the size of the evaporator may be reduced. This may bedone by increasing the amount of superheat maintained by the meteringdevice in proportion to the difference between heat load and compressorcapacity.

Therefore, there is a need to provide an evaporation system withimproved cooling efficiency that uses commonly available and generallylow-cost metering devices. There is also a need for an improved systemand method for regulating the flow of refrigerant into the evaporatorcoil of a variable-capacity evaporator system operating from a powersupply of limited capacity.

Referring to FIG. 1, an evaporator system 10 is configured to providecooling capabilities to the surrounding environment around. Theevaporator system 10 generally is coupled to a compressor 12 (e.g., avariable speed compressor) that provides refrigerant to an expansionvalve 14. The expansion valve 14 is typically coupled to an inlet 16 viaa flow restricting device 18 to feed the refrigerant to an evaporator 20and an outlet 22. The expansion valve is a an exemplary embodiment of ametering device or flow regulating device for regulating the flow fromthe compressor to the evaporator.

The compressor 12 is typically a variable speed compressor, butaccording to other exemplary embodiments may be a fixed speedcompressor. According to various exemplary embodiments, the compressor12 (i.e., variable speed or fixed speed) may be any be of any past,present, or future design capable of providing refrigerant in theevaporator system 10.

The thermal expansion valve 14 (e.g., an internally equalizedthermostatic expansion valve) is connected to supply fluid refrigerantto the inlet 16 of the evaporator 20. The expansion valve 14 may includea needle valve 24, a diaphragm 26, a pressure sensing bulb 28, and aninternal port 30. The flow of refrigerant is regulated by the needlevalve 24, which may move toward the fully open or fully closed positionsdepending on the differential pressure applied across the diaphragm 26.Pressure on one side of the diaphragm may be determined by thetemperature of the fluid-filled sensing bulb 28, which is coupled to theoutlet 22 of the evaporator 20. Pressure on the other side of thediaphragm may be based on the pressure at the internal port 30 locatednear the connection point to the evaporator inlet 16. According tovarious exemplary embodiments, the needle valve 24 may be of any past,present, or future valve design. According to other exemplaryembodiments, a ball valve, a globe valve, a diaphragm valve, a butterflyvalve, or any other valve capable of controlling fluid flow in theevaporator system 10 may be substituted for the needle valve.

The evaporator 20 is configured to provide a heat exchange area with theenvironment around it. Refrigerant (e.g., liquid refrigerant) is fedinto the evaporator 20 and flows near a heat source, for example theenvironment around the evaporator 20. In one embodiment, air is blownacross the evaporator coil by a blower or fan. A liquid refrigerant 32absorbs heat from the environment, thus cooling the environment andconverting the refrigerant into a gas 34. The gas exits the evaporatorvia the outlet 22 and returns to the compressor. According to variousexemplary embodiments, the evaporator 20 may include more or fewer thanthe illustrated number of coils. According to another exemplaryembodiment, a plate-type evaporator may be used.

Referring to FIG. 2, the initial superheat setting of the expansionvalve may be preset so that a small (e.g., 5 degrees F.) superheat ispresent when the evaporator system 10 is at maximum heat load and fullcompressor 12 speed. Under these conditions, the evaporator system 10may function in the conventional way, filling the evaporator 20 with theliquid refrigerant 32 so that the entire heat exchange capacity isavailable (i.e., greater liquid refrigerant 32 surface area and lessgaseous refrigerant 34 surface area).

Referring to FIG. 3, when the compressor 12 is slowed down, for exampleto save energy by reducing the power consumption of the evaporatorsystem 10, the reduced refrigerant flow across the flow restrictingdevice 18 results in an increase in the evaporator 20 superheat. Thisincrease in superheat effectively reduces the heat exchange area of theevaporator 20 (i.e., greater gaseous refrigerant 34 surface area andless liquid refrigerant 32 surface area). With less surface areaavailable to collect heat, the evaporator 20 temperature may fall. Thelower evaporator 20 temperature may cause the air flowing over thissmaller portion of the evaporator 20 to be colder than it wouldotherwise be if the evaporator 20 were operating with normal superheatin the conventional manner. Thus, evaporator system 10 may dynamicallychange the effective capacity of evaporator 20 in direct proportion tocompressor capacity and without regard to heat load. The resultingchange in operational characteristic of the evaporator system 10 may beparticularly advantageous to maintain the increased cooling capacitywhile reducing energy consumption during periods of sustained high heatload.

The flow restricting device 18 is located in the flow path from thethermal expansion valve 14 and the inlet 16 to the evaporator. The flowrestricting device 18 is intended to change the relationship of thepressure applied to one side of the diaphragm via the internal port 30and the pressure applied to the other side by the temperature sensingbulb 28. The restricting device 18 may increase the pressure of theinternal port 30 relative to that of the sensing bulb 28, effectivelyincreasing the flow of refrigerant into the evaporator 20 (thus reducingsuperheat) as the speed of the compressor increases. When the compressorslows down, the pressure drop created by the restricting device 18 isreduced and the pressure at the internal port 30 may more closely matchthe pressure of the evaporator 20.

The flow restricting device 18 may include an orifice in the flow path.The device 18 may also provide variable throttling to the refrigerantflow. For example, a throttle valve may be provided. The throttle valvemay be controllable (e.g., a solenoid valve) so that flow restriction isincreased at slower compressor speeds. is located in the flow path fromthe thermal expansion valve 14 and the the inlet 16 to the evaporator.

Although evaporator system 10 is illustrated as including multiplefeatures utilized in conjunction with one another, evaporator system 10may alternatively utilize more or less than all of the noted mechanismsor features. For example, in other exemplary embodiments, the flowrestricting device 18 may be a single unitary portion of expansion valve14. For example, an orifice located in the refrigerant outlet of theexpansion valve 14.

Although specific shapes of each element have been set forth in thedrawings, each element may be of any other shape that facilitates thefunction to be performed by that element. For example, sensing bulb 28is shown to be of a generally rectangular shaped cross-section, however,in other embodiments the structure may define that of a more curvilinearform.

For purposes of this disclosure, the term “coupled” means the joining oftwo components (electrical or mechanical) directly or indirectly to oneanother. Such joining may be stationary in nature or movable in nature.Such joining may be achieved with the two components (electrical ormechanical) and any additional intermediate members being integrallydefined as a single unitary body with one another or with the twocomponents or the two components and any additional member beingattached to one another. Such joining may be permanent in nature oralternatively may be removable or releasable in nature

The present disclosure has been described with reference to exampleembodiments, however workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the claimed subject matter. For example, although differentexample embodiments may have been described as including one or morefeatures providing one or more benefits, it is contemplated that thedescribed features may be interchanged with one another or alternativelybe combined with one another in the described example embodiments or inother alternative embodiments. Because the technology of the presentdisclosure is relatively complex, not all changes in the technology areforeseeable. The present disclosure described with reference to theexample embodiments and set forth in the following claims is manifestlyintended to be as broad as possible. For example, unless specificallyotherwise noted, the claims reciting a single particular element alsoencompass a plurality of such particular elements.

It is also important to note that the construction and arrangement ofthe elements of the system as shown in the preferred and other exemplaryembodiments is illustrative only. Although only a certain number ofembodiments have been described in detail in this disclosure, thoseskilled in the art who review this disclosure will readily appreciatethat many modifications are possible (e.g., variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter recited. For example,elements shown as integrally formed may be constructed of multiple partsor elements shown as multiple parts may be integrally formed, theoperation of the assemblies may be reversed or otherwise varied, thelength or width of the structures and/or members or connectors or otherelements of the system may be varied, the nature or number of adjustmentor attachment positions provided between the elements may be varied. Itshould be noted that the elements and/or assemblies of the system may beconstructed from any of a wide variety of materials that providesufficient strength or durability. Accordingly, all such modificationsare intended to be included within the scope of the present disclosure.Other substitutions, modifications, changes and omissions may be made inthe design, operating conditions and arrangement of the preferred andother exemplary embodiments without departing from the spirit of thepresent subject matter.

1. An air conditioning system comprising: an evaporator containingrefrigerant, wherein the evaporator is configured to exchange heat witha surrounding environment; a metering device for regulating the flow ofrefrigerant into the evaporator, wherein the metering device isconfigured to regulate the flow into the evaporator based, at least inpart, on the pressure sensed in a flow path to the evaporator; acompressor for compressing refrigerant and providing liquid refrigerantto the metering device; wherein the system is configured so thatrefrigerant flowing from the metering device into the evaporator passesthrough a flow restricting device located in the flow path.
 2. Thesystem of claim 1, wherein the compressor is a variable speedcompressor.
 3. The system of claim 2, wherein the speed of thecompressor is regulated based on an available power supply.
 4. Thesystem of claim 1, wherein the metering device includes a thermalexpansion valve.
 5. The system of claim 4, wherein the thermal expansionvalve includes a needle valve.
 6. The system of claim 1, wherein themetering device is controlled based on, at least in part, a temperaturesensed at an outlet of the evaporator.
 7. The system of claim 1, whereinthe flow restricting device comprises a throttle valve in therefrigerant flow path from the thermal expansion valve to theevaporator.
 8. The system of claim 1, wherein the flow restrictingdevice comprises an orifice.
 9. An air conditioning system including avariable speed compressor configured to operate at faster and slowerspeeds, an evaporator and a thermal expansion valve for regulating theflow of a refrigerant from the compressor to the evaporator, wherein thethermal expansion valve is configured to control the flow of therefrigerant into the evaporator based on a temperature sensed at theoutlet of the evaporator and a pressure sensed at the inlet to theevaporator; wherein the system includes a flow restricting device in aflow path from the thermal expansion valve to the evaporator therebyincreasing the efficiency of the system when the compressor is operatingat slower speeds.
 10. The system of claim 9, wherein the flowrestriction device is configured to throttle flow to the evaporator sothat when the compressor is operating at faster speeds refrigerant flowto the evaporator is not restricted.